Exothermic chromium compound containing composition and method of making same



W r 2,854,326 Patented Sept. 30, 1958 EXOTHERMIC cHRoMuJM COMPOUND CON- TAINING COMPOSITION AND METHOD or MAKING SAME Tom S. Perrin and Howard E. Ever-son, Painesville, Ohio, assignors to Diamond Alkali Company, Cleveiand, Ohio, a corporation of Delaware No Drawing. Application February 12, 1954 Serial No.-410,041

26 Claims. (Cl; 75-27) mium of the steel. may be obtained bydissolving an alloy such as ferrochromium in the molten steel bath. The procedure of dissolving the alloy in'the bath, however, has distinct disadvantages to the steelmaker, in that the time required to dissolve an alloy such as ferrochromium in: the bath is excessive, during, which time there is danger that the bath composition will change; For example, the bath may become contaminated by nitrogen absorbed I from the furnace atmosphere, and if an electric arc furnace is used, there is additional likelihood of carbon being absorbed into the bath.

The art, therefore, has sought other means for introducing chromium into alloy baths. One such means is a composition containing a chromium alloy, an oxidizing agent, and a reducing agent comprising slag-forming components. By properly combining, the components of. such a composition, the exothermic reaction of oxidizing and reducing agents may generate sufficient heat' to pro-- vide molten chromium or an alloy thereof in contact with the steel bath, whereby rapid solution. of chromium, or the alloy, in the bath takes place.

Compositions of matter which undergo anexothermic chemical reaction to produce metallic elements and alloys, referred to in the art as trate, or sodium chlorate, together with a reducing: agent, such as silicon, calcium, aluminum, and magnesium, either alone or in the form of an alloy with ferrous or non-ferrous metals. Such exothermic mixes have been used in the manufacture of steel for the purpose of introducing chromium and other metallic elements into a molten steel bath, either in. the furnace or inthe ladle.

The difficulties encountered in the manufacture of steel with the prior art exothermic mixes containing sodium nitrate includes the introduction of nitrogen into the molten steel bath, which nitrogen,v if excessive, in some types of chromium-bearing steels, causes the ingots poured from the bath to rise in the mold and bleed, even where such exothermic mixes. may be used in. the production of relatively low chromium-containing, steel.

Usually, in the use of oxidizing agents such as sodium nitrate, sodium or potassium chlorate, and the like, the chromium in the exothermic mixes isv associatedwith. one or more components of thereducingagent-inthe form ofsanalloy, such as commercial grades ofaferrochrome silicon (Cr 35%-40%, Si 42%50%), wherein silicon exothermic mixes, have in general included an oxidizing agent, such as sodium n1- is the slag-forming component and the reducing agent. Other metals, such as Ca and Al, may also be included in the form of their alloys, such as calcium silicide, or ferrochrome silicon aluminum, and the like, as slag-forming and reducing agent components.

The problem faced in the art has been one of providing exothermic mixes containing low cost sources of chromium and oxidizing agents which do not produce deleterious gases in the steel. bath, while-providing a reaction sufiiciently exothermic that chilling of the steel bath is not encountered. I

The present invention is based in part upon the finding that complex chromiumcompounds may be-produced by the reaction of analkali metal chromate with substances, such as hydrogen, carbon, carbon monoxide, or compounds having hydrogen chemically combined with carbon, in a non-oxidizing atmosphere, which compounds are apparently in a state of oxidation intermediate that of the trivalent and hexavalent forms of chromium. Further, the present invention is based' upon the finding that such reaction products will, under proper conditions, react exothermically with certain metal or metalloid reducing agents to produce metallic chromium, and that such reaction is sufliciently'exotheric to be useful either in the recovery of chromium metal as such, or in combination with other alloying elements, such as in the manufacture of chromium-bearing steel.

The said complex chromium compounds, upon which the present invention is based in part, appear to be a chemical combination of two or more chromium-containingcomponents which are already saturated according to the classical concepts ofvalency. Such complexes are believedto contain chromium in a valence state intermediate the normal trivalent and hexavalent states of this element, since they may be characterized by," (1) their ability to yield both trivalent and hexavalent chromium compoundson being calcined at temperatures of the order ofabout 980-l000 C. in an oxidizing atmosphere,

(2) their relative chemical inertness. except under strong.

oxidizing conditions, (3) insolubility in water, and (4) other properties which are not characteristic of physical mixturesof trivalent and hexavalent chromium compounds.

One of the objects of the present invention isto provide exothermic mixes containing complex chromiumcompounds wherein the chromium is apparently in an intermediate state of oxidation between that of trivalent and hexavalent chromium, whereby the oxidizing agent of the exothermic mix is: used as a source of chromium and contamination by deleterious gases of the metal produced is prevented.

Another object ofthe invention is to provide an exothermic mix from which chromium metal may be recovered alone or in combination: with. other metals in an alloy solution.

These and other objects of the inventionwill be apparent from the description of the invention given hereinbe1ow.-

Pursuant to the above objects, the present invention includes exothermic alloying compositions comprising, as the oxidizing agent thereof, a. complex'chromium compound obtained by thereaction of an alkali metal chromate, in the form of a solid, asopposed to a solution,

Witha substance-selected from the group consisting of hydrogen, carbon, carbon monoxide, and compounds having hydrogen chemically combined with carbon, in a nonox-idizing atmosphere, and comprising. as thereducing agent thereof at least one element from the group consisting of alkaline earth metals, Al, and Si. The invention also includes the method of recovering chromium Y which comprises mixing'a complex chromium compound obtained by the reaction of an alkali metal chromate,

in the form of a solid, as opposed to a solution, with a substance selected from the group consisting of hydrogen, carbon, carbon monoxide, and compounds having hydrogen chemically combined with carbon, in a non-oxidizing atmosphere, with at least one element selected from the group consisting of alkaline earthmetals, Al, and Si, heating, the mixture to effect reaction between said reaction product, and an element of said group, and recovering chromium from the reaction products of said mixture. The term alkaline earth metals refers to the group II elements, Mg, Ca, Sr, Ba, and Rad The order ofpreference for the alkaline earth metals in the present invention is Ca, Mg, Sr, Ba, and Ra.

The complex chromium compounds which are products obtained by the solid-phase reaction of an alkali metal chromate with a substance selected from the group consisting of hydrogen, carbon, carbon monoxide, and compounds having hydrogen chemically combined with carbon, in a non-oxidizing atmosphere, may be obtained from any one of the alkali metal chromates,such as lithium, sodium, potassium, rubidium, and cesium chromate. Preferably, however, for the purposes of the present invention, such reaction products are obtained by the solid-phase reaction of sodium chromate with hydrogen or a compound having hydrogen chemically combined with carbon. These reaction products are preferably obtained at temperatures above 250 C., and below the fusion point of the reaction mass. 1

Hydrogen, which may be employed in thepreparatio n of the preferred complex reaction product, may be derived from any suitable source of hydrogen, such as from the electrolysis of sodium chloride brine or other aqueous solution of an electrolyte. Similarly, the carbon, carbon monoxide, or compounds containing hydrogen chemically combined with carbon may be any suitable material readily entering into reaction with the solid alkali metal chromate, such as, for example, charcoal, graphite, coke, producer gas, coke oven gas, carbohydrates, of which sawdust, wood flour, sugars, starch, and the like are representative, and hydrocarbons, preferably in the gaseous state, of which the lower aliphatic hydrocarbons, both saturated and unsaturated, are representative, may be employed. The solid-phase reaction product of an alkali metal chromatewith carbon, or one of the above carbon compounds, may suitably be used where the introduction of carbon into the steel bath is not deleterious.

The metalloid and metal reducing agents, as noted hereinabove, include the alkaline earth metals, Mg, Ca, Sr, Ba, and Ra, as well as Al and Si. These reducing agents, hereinafter referred to as reductants, may, if desired, be employed alone, but preferably are employed in combination with other metallic elements as alloys, and especially suitable are those alloys in which silicon is present. Thus, alloys such as the various commercial forms of ferrosilicon, ferrochrome silicon, ferrochrome silicon aluminum, ferrosilicon aluminum '(Alsifer), aluminum silicide, calcium silicide, calcium aluminum silicide, and the like, may be used.

In order to determine the amount of reductant which may suitably be employed in the compositions and'in the practice of the method of the present invention, the oxi-Q dizing power of the complex chromium compounds which may conveniently be considered as available for reaction with the above-noted reducing agents is computed by arbitrarily converting the Cr content of the complex chromium compounds to Cr O and proportioning the calculated amount of oxygen available therefrom to the amounts of the reductants with which it may be combined.

Thus, for example, if a chromium complex material were prepared as described hereinabove, and were found to contain 54.7% Cr (total) this would be the equivalent of 80% Cr O which would be taken (arbitrarily) to represent the portion of the chromium complex material availablefor oxidizing the reducing agents. If then the significant components of the reductant were Al and Si, for example, it might be desirable to proportion the Al component to the equivalent of /3 the Cr O and the Si to the equivalent of /a the Cr O Since the reactions involved may be represented thus:

Cr O +2Al=2Cr+A] O and 2Cr O +3Si=4Cr+3SiO the computations are conveniently set up thus:

(3)(28)(Amt. CrQO) WWW/(S1) The amounts of the components of the reductant indicated by such computation (x and y) are preferably increased by a factor within the range of 1.1 to 2.5, suitably by a factor of 1.5 to 1.75.

One reason for employing an excess of the reductant over the calculated amount for the complex chromium compounds arises, in part, from the fact that oxygen combined with chromium in the complex chromium compounds is in excess of that required to satisfy the formula Cr O and. the chromium, therefore, as noted above, would appear to be in a valence state intermediate that of the normal trivalent or hexavalent state, or possibly to be comined with oxygen and alkali metal in some coordinate co-valent state. Another reason arises when silicon is used as one of the components of the reductant. There is evidence reported in the chemical literature indicating that reaction of oxygen-bearing compounds and silicon at high temperatures may result in silicon-oxygen compounds having less than two atoms of oxygen per atom of silicon.

The higher recovery of chromium where the excess of reductants, as computed above, is of the order of 1.5 to 1.75, would tend to indicate that the first of" these reasons is sound, and where silicon is one component of the reductants, that the second reason may also be sound. In the preparation of the compositions of the present inventlon, as well as inthe method thereof, the complex chromium compounds, and the reductants, are prefer ably in a finely-divided state,- and are mixed together so as to form uniform dispersion of both components. The mixture may be combined with a suitable binding agent and subjected to mechanical agglomeration, as by briquetting or pelletizing, or may be used in the form of loose, free-flowing powder.

Where the compositions of the present invention are employed as a means of making final adjustments in the chromium content of steel in the ladle, such compositions are preferably in the form of a loose, free-flowing powder. Where larger amounts of chromium are desired in ladle additions, the compositions of the present invention may be used in the form of briquettes, for example, by placing the briquettes in the ladle prior to tapping the steel into the ladle.

In order that those skilled in the art may better understand the nature of the compositions and the method of the present invention, and in what manner the same may be carried into effect, the following specific examples are offered EXAMPLE I Part A The reaction product is recovered from the a tubular reactor chamber and leached with hot water in order to remove sodium hydroxide and other by-products formed by the reaction. The leached material, when dried, is a brownish, gray-green powder.

Part B A second portion of 100 parts of sodium chromate crystals is mixed with parts of sawdust-and the mixture transferred to a reactor. Air is swept from the reactor, which is then heated by means of .a gas burner until a reaction between the chromate and sawdust is initiated, and heating of the reactor is then stopped. The reaction continues substantially to completion spontaneously. The reaction product is thoroughly leached with hot water as in Part A above and the leached residue dried, giving a somewhat darker, gray-green powder.

Part C .100 parts of sodium chromate crystals are mixed with 30 parts of sawdust, and the mixture of sodium chromate and sawdust placed in a tubular reactor. Hydrogen .gas is passed over the mixture while the mass is indirectly heated to a temperature of about 315 to 400 C., until the reaction is complete. The reaction product is treated as described in (A) and (B) above, and the dry product obtained resembles that of Part .A hereof in color and texture.

Pa'rt D 100 parts of sodium chromate crystals are combined with 2 /2 equivalents of carbon in the form of finelydivided charcoal, and the mixture thus obtained transferred to a tubular reactor wherein the mixture is indirectly heated sufficiently to initiate the reaction, which thereafter proceeds with the generation of sufficient heat to maintain the reaction. The dry product obtained has a dark, gray-green appearance, and the texture indicates the presence of unreacted carbon.

25 parts of each of the above-described reaction prodnets are combined with 14 parts of ferrosilicon (75% Si) and heated in an induction furnace to a red heat. After a few minutes at the red heat, the reaction proceeds very rapidly, as evidenced by the masses becoming suddenly white hot and fusing. The fused reaction masses are cooled and, in each case, a button of chromium-iron alloy and many fine particles of metal are found in the cooled solidified mass.

EXAMPLE II A dry mixture containing approximately 75% sodium chromate, 15% sodium aluminate, and 10% free alkali, calculated .as NaOH, is placedin a tubular reactor, wherein it is maintained quiescent, while a stream of hydrogen gas is passed over the mixture, and it is heated to a temperature of 370 C. The flow of hydrogen gas, at all times in excess of that required to react with the sodium chromate in the mixture and heating at the stated temperature, are continued for about 1 hour. At the end I of this time, the reaction product obtained is removed from the reactor, cooled, leached with hot water to remove soluble compounds, and the leached residue is dried and analyzed; the analysis for total chromium, computed in terms of Cr O is 74% Cr O Calcination of a portion of the leached product in an oxidizing atmosphere at 1000 C. yields a calcined material which analyzes 49.5% sodium chromate and 50.5% Cr O Fifty parts of the uncalcined reaction product are mixed with 13.5 parts of finely-ground silicon (passes Tyler Standard 100 mesh screen, 0.0058 inch openings), and are placed in a crucible and heated in an induction furnace to a dull red heat, whereupon the sourceof power to the furnace is out 01f.

Within a few minutes, the mixture in the crucible appears to be undergoing reaction, in that it changes from a dull red to bright red, and then back to dull red again.

When the reaction mass in the crucible is cooled and broken apart, many small pellets of metal, identified as chromium, are recovered. in terms of the computed Cr O content of the uncalcined reaction product, the Si is in excess by a factor of 1.3.

EXAMPLE III 21 parts of iron punchings are placed in 'thecrucible of a high frequency induction furnace and melted. Furnace additions of 0.3% silicon as ferrosilicon, and 0.5% manganese as ferromanganese are made'when the melt reaches about 1590 C. Within about /2 minute after the addition of the silicon and manganese, a sample is poured for chemical analysis. After pouring the base metal sample, the temperature of is allowed to rise again toabout 1590 C., and the .power adjusted to maintain this temperature.

A reaction product obtained from sodium chromate and hydrogen, as described in Part A of ExampleI above, is analyzed and, for convenience, the values for Cr and Na are computed in terms of Cr O and Na O. These values are found to be:

Percent Na O that required to react with the computed Cr O content of the reaction product is 1.2 for Al and 2'for Si. With the temperature of the steel bath at about l5901650 C., 1.08 parts of the exothermic mixture are added to the bath as a loose powder and allowed to react. action is rapid and the slag fluid. 'The molten metal bath is tapped into a ladle from which an ingot is poured. Analysis of the ingot shows that the silicon content of the steel has remained constant at 0.25% during the reaction of the exothermic mixture, and that the percentage of chromium incorporated in the steel is 1.84%, representing an 87.8% recovery of chromium from the exothermic mixture. During the course of "the reaction of the exothermic mixture in the furnace, a temperature rise of 50 C. is noted.

EXAMPLE IV Following essentially the same procedure as that described in Example III above, for the addition of silicon and manganese, a heat is prepared'consisting of parts of ingot iron, and sufficient ferrosilicon and ferromanganese added thereto to provide 0.25% silicon and 0.35% manganese in the metal bath, is charged to a high frequency induction furnace.

2.2 parts of the reaction product of sodium chromate and hydrogen, which reacton product, upon analysis and computing the Cr and Na in terms of Cr O and Na O as in Example II, gives Cr O 77.7% and Na O, 13.2%, are dry-mixed with calcium chromate, 0.93 part, atomized aluminum 0.70 part, and ferrochrome silicon, 1.32 parts, giving 5.15 parts of an exothermic mix containing 38.8% Cr. The Al is proportioned so as to be equivalent to 1.5 times the CaCrO plus about 0.5 of the computed Cr O content of the complex. The Si is proportioned so as to be equivalent to 1.2 times the computed Cr 'O content of the chromium complex.

After the temperature of the molten metal bath in the furnace has reached 1590 C., the furnace is tapped for a sample for analysis, which analysis shows that the bath contains 0.22% silicon and 0.02% chromium. The bath in the furnace is heated to a temperature of 1760 the metal in the furnace The re- 7 C., and about /2 ofthe bath is tapped into a preheated ladle. 5.15 parts of the exothermic mixture described above are then introduced into the ladle in loose powder form, whereupon the reaction is initiated, and is found to be complete within about /2 minute.

the furnace contents is then tapped into the ladle. The

, slag produced by the exothermic mix is fluid and analysis of the bath in the ladle shows that the silicon content thereof, after the addition of the exothermic mixture, is

, 0.34%, and that the chromium contentthereof is 1.72%,

showing an 87.5% recovery of the chromium in the exothermic mixture. The total amount of all metal re 1 covered from the furnace and ladle is 103 parts.

EXAMPLE v Following the procedure ofExample 1V above, 200

The remainder of Example II, gives Cr O 70.7%. and -Na O, 23.6% is dry-mixed with 6.3 parts of calcium chromate 3.0 parts of atomized aluminum, and 17.6 parts of ferrochrome silicon to make an exothermic mixture containing 40.5% Cr.

About /2 of the molten metal bath, at about 1760 C., istapped into a preheated ladle. The exothermic mixture in loose form is then placed on top ofthe metaL,

Reaction is initiated substantially immediately and the reaction completed within about 2 minutes, yielding a fluid slag. The remainderof the bath in the furnace is.

tapped into the ladle. The amount of aluminum added in the exothermic mixture is proportioned to be equivalent to 1.5 times the calcium chromatepresent. The amount 1 of silicon added as ferrochrome silicon in the exothermic .mix is proportioned to be equivalent to about 1.5 times the computed Cr o of the chromium complex. A sample of the final bath is tapped from the ladle and analyzed. The analysis shows 0.08% carbon, 1.81% silicon, and 9.40% chromium, representing a 96.1% recovery of chromium from the exothermic mixture.

While there have been described various embodiments of the inventon, the methods and products described are not intended to be understood as limiting the scope of the invention as it is realized that changes therewithin are possible and it is further intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. An exothermic composition comprising as the oxidizing agent thereof the reacton product obtained by the solid-phase reaction, in a non-oxidizing atmosphere, of an alkali metal chromate with a substance selected from the group consisting of hydrogen, carbon, carbon monoxide, and compounds having hydrogen chemically combined with carbon, at a temperature above about 250 C. and below the fusion point of the reaction mass, the chromium of said reaction product being in an intermediate state of oxidation between that of trivalent and hexavalent chromium, and comprising as the reducing agent thereof an element selected from the group consisting of the alkaline earth metals, Al, and Si.

2. The composition of claim 1 in which the oxidizing agent thereof is the reaction product obtained by the solid-phase reaction of an alkali metal chromate with hydrogen.

3. The composition of claim 1 in which the oxidizing agent thereof is the reaction product obtained by the rnium of said reaction product beingin an intermediate solid-phase reaction of an alkali metal chromate with carbon.

4. The composition of claim 1 in which the oxidizing agent thereof is the reaction product obtained by the solid-phase reaction of: an alkali metal chromate with carbon monoxide.

5. The composition of claim 1 in which the oxidizing agent thereof is the reaction product obtained by the solid-phase reaction of an alkali metal chromate with a compound having hydrogen chemically combined with carbon.

6. The composition of claim 1 inwhich the alkali metal chromate is sodium chromate.

7. The composition of claim 6 in which the oxidizing agent thereof is the reaction product obtained by the solid-phase reaction of sodium chromate with hydrogen. 8. The compositionof claim 6 in which the oxidizing agent thereof is the reaction product obtained by the solid-phase reaction of sodium chromate with carbon.

9. The composition of claim 6 in which the oxidizing agent thereof is the reaction product obtainedby the solid-phase reaction of sodium chromate with carbon monoxide.

10. The composition of claim 6 in which theoxidizing agent thereof is the reaction product obtained by the solidrphase reactionof sodium chromate and a compound having hydrogen chemically combined with carbon.

11. The method of recovering chromium which ineludes mixing the reaction product obtained by the solidphase reaction, in a non-oxidizing atmosphere, of an alkali metal chromate and a substance selected from the group consisting of hydrogen, carbon, carbon monoxide,

and a compound having hydrogen chemically combined with carbon,.at a temperature above about 250 C., and below the fusion point of the reaction mass, the chro state of oxidation between that of trivalent and hexavalent chromium, with at least one element selected from the group consisting of the alkaline earth metals, A1, and Si, and heating the mixture to effect reaction between said reaction product and said element of said group.

12. The method of claim 11 in which said reaction product is obtained by reaction of an alkali metal chromate with hydrogen.

13. The method of claim 11 in which said reaction product is obtained by reaction of an alkali metal chromate with carbon.

14. The method of claim 11 in which said reaction product is obtained by reaction of an alkali metal chromate with carbon monoxide.

15. The method of claim 11 in which said reaction product is obtained by reaction of an alkali metal chromate and a compound having hydrogen chemically combined with carbon.

16. The methodo'f claim 11 wherein the alkali metal chromate is sodium chromate.

17. The method of claim 16 wherein said reaction product is obtained by the reaction of sodium chromate with hydrogen.

18. The method of claim 16 wherein said reaction product is obtained by reaction of soduim chromate with carbon.

19. The method of claim 16 wherein said reaction product is obtained by reaction of sodium chromate with. carbon monoxide.

20. The method of claim 16 wherein said reaction product is obtained by reaction of sodium chromate and a compound having hydrogen chemically combined with carbon.

21. The method of manufacturing a chromium-bearing alloy, which includes the steps of reacting, in a nonoxidizing atmosphere, solid sodium chromate with a substance selected from the group consisting of hydrogen, carbon, carbon monoxide, and compounds having hydrogen chemically combined with carbon, at a tempcramm above about 250 C., and below the fusion point of the reaction mass, the chromium of the reaction product thus obtained being in an intermediate state of oxidation between that of trivalent and hexavalent chromium, combining said reaction product with non-carbonaceous reducing agents selected from the group consisting of the alkaline earth metals, A1 and Si, the amount of said reducing agents being within the range of 1.1 to 2.5 times that amount equivalent to the available oxygen of said reaction product, said available oxygen being computed as Cr O from the total Cr content of said reaction prodnot, and heating the mixture to effect reaction between said reaction product and said reducing agents.

22. The method of claim 21 in which the substance selected from said group is hydrogen, and said reducing 15 agents include silicon.

23. The method of claim 22 in which said reducing agents include ferrosilicon.

24. The method of claim 22 in which said reducing agents include an alloy of Ca and Si.

25. The method of claim 22 in which said reducing agents include A1. a

26. The method of claim 22 in which said reducing agents include an alloy of Al, Si, and Fe.

References Cited in the file of this patent UNITED STATES PATENTS 

1. AN EXOTHERMIC COMPOSITION COMPRISING AS THE OXIDIZING AGENT THEREOF THE REACTON PRODUCT OBTAINED BY THE SOLID-PHASE REACTION, IN A NON-OXIDIZING ATMOSPHERE, OF AN ALKALI METAL CHROMATE WITH A SUBSTANCE SELECTED FROM THE GROUP CONSISTING OF HYDROGE, CARBON, CARBON MONOXIDE, AND COMPOUNDS HAVING HYDROGEN CHEMICALLY COMBINED WITH CARBON, AT A TEMPERATURE ABOVE ABOUT 250*C. AND BELOW THE FUSION POINT OF THE REACTION MASS, THE CHROMIUM OF SAID REACTION PRODUCT BEING IN AN INTERMEDIATE STATE OF OXIDATION BETWEEN THAT OF TRIVALENT AND HEXAVALENT CHROMIUM, AND COMPRISING AS THE RECUCING AGENT THE ALKALINE EARTH METALS, AL, AND SI. 